Now that we have worked with services and notifications separately, we are all ready to use the two together to make a real service that is notified to the user through a status bar update that the service is running. The status bar removes the notification as soon as the service is stopped.

In this program, I also increment a counter once the service starts to show that the service is continuously running in the background while we do other work. When we stop the service we are able to see the updated count.

Let us look at the code:

I have created a class NotifyService which extends the service class. This is the service class that will be started through the activity – ServiceLauncher

Now let us see what the service does?

It does 3 things – Toast a message that the service has started. Update the status bar with a notification. Finally start incrementing the counter. All this is done in the onCreate() method of the NotifyService Class

Toast.makeText(this,"Service created at " + time.getTime(), Toast.LENGTH_LONG).show();

showNotification();           

            incrementCounter();

Here is the showNotification() Method:

    private void showNotification() {

 CharSequence text = getText(R.string.service_started);

 Notification notification = new Notification(R.drawable.android, text,System.currentTimeMillis());

 PendingIntent contentIntent = PendingIntent.getActivity(this, 0,

                new Intent(this, ServiceLauncher.class), 0);

notification.setLatestEventInfo(this, getText(R.string.service_label),

      text, contentIntent);

nm.notify(R.string.service_started, notification);

    }

Finally, here is the method for incrementing the counter incrementCounter():

    private void incrementCounter() {

timer.scheduleAtFixedRate(new TimerTask(){ public void run() {counter++;}}, 0, 1000L);

    } 

On stopping the service, it obviously has to do the reverse actions: stop the counter, remove the status bar notification and then toast a message to the end user saying the service has stopped! So here it is:

      shutdownCounter();

      nm.cancel(R.string.service_started);

      Toast.makeText(this, "Service destroyed at " + time.getTime() + "; counter is at: " + counter, Toast.LENGTH_LONG).show();

      counter=null;

This is the code in the onDestroy() method in the NotifyService class.

With this the service is ready. But we need to be able to start this service and stop it. This I have done through a ServiceLauncher class just as I had done in the previous part of this series. You can get the complete code here.

August 04, 2011

So far, in all my examples, I have been using the declarative way of creating an Android UI using XML. However, there could arise certain situations when you may have to create UI programmatically. Sincere advice would be to avoid such a design since android has a wonderful architecture where the UI and the program are well separated. However, for those few exceptional cases where we may need too… here is how we do it.

Every single view or viewgroup element has an equivalent java class in the SDK. The structure and naming of the classes and methods is very similar to the XML vocabulary that we are used to so far.

Let us start with a LinearLayout. How would we declare it in an XML?

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:orientation="vertical"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    >

<TextView 

    android:layout_width="fill_parent"

    android:layout_height="wrap_content"

    android:text="@string/hello"

    />

</LinearLayout>

This just contains a TextView embedded in a LinearLayout. A very trivial example. But serves the purpose intended. Let me show how almost every single element here corresponds to a class or a method call in the class.  So the equivalent code in the onCreate(…)  method of an activity would be like this:

         super.onCreate(savedInstanceState);

      

        lLayout = new LinearLayout(this);

        lLayout.setOrientation(LinearLayout.VERTICAL);

        //-1(LayoutParams.MATCH_PARENT) is fill_parent or match_parent since API level 8

        //-2(LayoutParams.WRAP_CONTENT) is wrap_content

        lLayout.setLayoutParams(new LayoutParams(

LayoutParams.MATCH_PARENT,

LayoutParams.MATCH_PARENT));

        tView = new TextView(this);

        tView.setText("Hello, This is a view created programmatically! " +

                  "You CANNOT change me that easily :-)");

        tView.setLayoutParams(new LayoutParams(

LayoutParams.MATCH_PARENT,

LayoutParams.WRAP_CONTENT));

        lLayout.addView(tView);

        setContentView(lLayout);

Like this any layout view can be created. But from this small example you can notice two outstanding things – very tedious to code for every attribute of the view. And any simple change in the view, you need to change the code, compile, deploy and only then you see the effect of the change – unlike in a layout editor. 

April 23, 2011

We have seen that we can declare User Interface in Android through XML or we can even create the UI Programmatically. Now, we will see how we can mix the two and use it for building dynamic User Interfaces. One example of such a case would be when on a particular action of the user on one of the UI elements, you need more UI elements to appear on the same screen. How do we achieve this?

You can do it in two ways:

1.       The dynamic part of the UI can be created programmatically. However we saw in my earlier tutorial that it is not a very good way to mix UI and code.  So, we can

2.       Define the dynamic UI too as an XML and use XML inflation to include it into the existing UI.

We will see how to do the 2^nd way, which probably is a good practice too.

As always, again a very simple example. Assume I have a very simple linear layout. In that I want to include a button. I can do it as part of the mail XML itself. However, assume that this button is supposed to be reused in many activities and hence I have defined it as a separate XML. How do I include it into the main XML?

So, here is the main.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:orientation="vertical"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:id="@+id/layout1"

    >

</LinearLayout>

Here is the buttons.xml that is also created in the res/layout folder:

<?xml version="1.0" encoding="utf-8"?>

<Button xmlns:android="http://schemas.android.com/apk/res/android"

        android:id="@+id/button_small_left"

 style="?android:attr/buttonStyleSmall"

        android:text="Press to close"

    android:layout_width="wrap_content"

    android:layout_height="wrap_content"/>

And here is the Activity’s onCreate(…) method of the InflateView class:

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        final LayoutInflater  inflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        Button b = (Button)inflater.inflate(R.layout.buttons,

                null);

       

        lLayout = (LinearLayout)findViewById(R.id.layout1);

        lLayout.addView(b);

First 3 lines must be familiar. In the 4^th line, I am getting a handle to the LayoutInflater through the getSystemService(…) method.  This inflater has a method inflate to which I pass the buttons.xml by passing the parameter R.layout.buttons. Then, I try to append this button to the Linear Layout that already exists and is set as the view in line 2 setContentView(R.layout.main). How to append? I get a handle to the LinearLayout lLayout and add the new button to it in the last line!

That simple to inflate an XML and append it to an existing view!

However, I have gone ahead and added another bit to this program as shown below:

        b.setOnClickListener(new OnClickListener() {

           

            public void onClick(View v) {

                  //restrict to adding only 1 textview child element

                  if (lLayout.getChildAt(2) == null)

                  {

                  TextView tv = (TextView)inflater.inflate(R.layout.text, null);

                  lLayout.addView(tv);

                  }

            }

        });

On the click of this dynamically added button, I am showing how we can add more to the UI dynamically through inflation. Assume, on the click of the button, you want to show some new text. This TextView is defined in another XML called text.xml which is also in the res/layout folder.

So, I am inflating from this XML and appending it to the LinearLayout view. So, a lot can be achieved for dynamic UI through inflation.

April 23, 2011

The concept of Broadcast Receivers, one of the fundamental blocks of Android, is very simple. These are applications that will respond to any intent that is broadcast by other applications. Provided the broadcast intent matches the intent specified against the receiver in the AndroidManifest.xml

This goes to automatically imply that many activities, events, services or the like can broadcast intents expecting the appropriate action to be automatically taken. So, to begin with, let us see the various Broadcast events that are given by the platform itself. Here is a standard list obtained from the android documentation:

·         ACTION_TIME_TICK

·         ACTION_TIME_CHANGED

·         ACTION_TIMEZONE_CHANGED

·         ACTION_BOOT_COMPLETED

·         ACTION_PACKAGE_ADDED

·         ACTION_PACKAGE_CHANGED

·         ACTION_PACKAGE_REMOVED

·         ACTION_PACKAGE_RESTARTED

·         ACTION_PACKAGE_DATA_CLEARED

·         ACTION_UID_REMOVED

·         ACTION_BATTERY_CHANGED

·         ACTION_POWER_CONNECTED

·         ACTION_POWER_DISCONNECTED

·         ACTION_SHUTDOWN

For details on when each of these intents get broadcasted, please see the android documentation. I have chosen the BROADCAST event ACTION_TIME_CHANGED as I can simulate a time change in the emulator. How to simulate the time change from adb shell is given at the end of this tutorial.

Now let us get on to the example of a broadcast receiver. You can download the complete code here.

Any activity that intends to respond to broadcasts has to extend the android.content.BroadcastReceiver class and implement the single method onReceive().

In my example, I just notify on the status bar that the time has changed and the moment the user clicks on the status bar and sees the details, clicks on the details, the notification is removed from the status bar.

When the user clicks on the detailed portion, I take the user to the contacts application, just for anything better. Ideally this should take to an activity relevant to the application. So, if you see the onReceive() method, it is nothing but a notification example. That is all.

      private NotificationManager mNotificationManager;

      private int SIMPLE_NOTFICATION_ID;

     

      @Override

      public void onReceive(Context context, Intent intent) {

        mNotificationManager = (NotificationManager)context.getSystemService(Context.NOTIFICATION_SERVICE);

      Notification notifyDetails = new Notification(R.drawable.android,"Time Reset!",System.currentTimeMillis());

      PendingIntent myIntent = PendingIntent.getActivity(context, 0, new Intent(Intent.ACTION_VIEW, People.CONTENT_URI), 0);

      notifyDetails.setLatestEventInfo(context, "Time has been Reset", "Click on me to view Contacts", myIntent);

      notifyDetails.flags |= Notification.FLAG_AUTO_CANCEL;

      mNotificationManager.notify(SIMPLE_NOTFICATION_ID, notifyDetails);

            Log.i(getClass().getSimpleName(),"Sucessfully Changed Time");

      }

Once this class is ready, start the android emulator in eclipse. Then, simulate a time changed from the command prompt as given below. You will see the notification come up.

Simulating a time change in the emulator:

To start the adb shell type (in windows, assuming the path has been set to the tools folder of android sdk installation):

C:\> adb shell

#date –- 2009-10-01 14:24:59

20070325.123456

#date –s 20070325.123456

The first step date –- gives the time in seconds since Jan 1^st 1970. Take the result and give it as a parameter to date –s, the time is reset in adb and within a minute on the android emulator. This broadcasts the event that time has been changed in the emulator and kicks off the Broadcast Receiver program that has been executed.

April 20, 2011